EP0221381A2 - Electrochemical gas sensor - Google Patents
Electrochemical gas sensor Download PDFInfo
- Publication number
- EP0221381A2 EP0221381A2 EP86113890A EP86113890A EP0221381A2 EP 0221381 A2 EP0221381 A2 EP 0221381A2 EP 86113890 A EP86113890 A EP 86113890A EP 86113890 A EP86113890 A EP 86113890A EP 0221381 A2 EP0221381 A2 EP 0221381A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- electrolyte
- electrode
- sensing electrode
- platinum
- further characterized
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
- G01N27/4045—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen
Definitions
- This invention relates to electrochemical gas sensors and more particularly to a sensor for sensing alkyl sulfides and lewisite in a gaseous environment.
- U.S. Patent 4,184,937 which issued on January 22, 1980, to H. Tataria et al. entitled "Electrochemical Cell for the Detection of Chlorine", describes a three electrode cell with a non-aqueous electrolyte consisting preferably of lithium perchlorate dissolved in an organic solvent selected from the group consisting of gamma-butyrolactone and propylene carbonate.
- the non-aqueous electrolyte has a considerably lower freezing point and vapor pressure than an aqueous electrolyte.
- the electrodes for use in the two or three electrode electrochemical cells are comprised of either gold or platinum black.
- an aqueous sensor of the type described in U.S. Patent 3,776,832 to detect chemical warfare agents such as mustard gas (di (2-chloroethyl) sulfide, designated HD).
- chemical warfare agents such as mustard gas (di (2-chloroethyl) sulfide, designated HD).
- a sensor containing a caustic aqueous electrolyte in contact with a gold sensing electrode has been used to detect the presence of HD.
- the aqueous electrochemical sensor has three disadvantages when used for the detection of HD. First, the sensor is slow; it requires more than 30 minutes to reach its equilibrium current value at a given concentration of HD.
- the slow equilibration time is due to the fact that HD is not oxidized directly at the working electrode, but is converted to thiodiglycol in the electrolyte and then the alcohol functional group of the thiodiglycol is oxidized at the working electrode.
- the half life of the hydrolysis of HD to thiodiglycol is greater than five minutes.
- the sensor suffers from numerous false alarms, since the aqueous HD sensor is sensitive to aliphatic alcohols, aldehydes, and several other gases in addition to alkyl sulfides.
- the sensor has a relatively short life due to absorption of CO2 from the air by the caustic electrolyte.
- dialkyl sulfides similar to HD can be oxidized to form the corresponding sulfoxides and sulfones.
- An apparatus for detecting selected compounds in a gaseous environment comprising a sensing electrode including platinum or alloys thereof in contact with an electrolyte, the electrolyte being exposed to the gaseous environment, a reference electrode in contact with the electrolyte, and means for maintaining the potential of the sensing electrode with respect to the potential of the reference electrode, wherein the electrolyte includes a solution of ethylene glycol, water, and a halide, whereby said selected, for example, alkyl sulfides and LEWISITE compounds are oxidized at the sensing electrode.
- the electrolyte includes a solution of water and a halide.
- Electrochemical gas sensor 10 includes a reference electrode 11, a counter electrode 12 and a sensing electrode 13.
- Sensing electrode 13 may be attached to one side of a porous membrane 24 which may be for example tetrafluoroethylene. The other side of membrane 24 is exposed to the gaseous environment 34 to be monitored.
- Sensing electrode 13 may be for example a platinum wire mesh, a layer of platinum vacuum sputtered directly on to membrane 24, or a composite structure fabricated by sintering a mixture of platinum powder and small polytetrafloroethylene (PTFE) particles to membrane 24.
- Reference electrode 11, counter electrode 12, and sensing electrode 13 are spaced apart from each other and in contact with electrolyte 14.
- Reference electrode 11 and counter electrode 12 may be positioned edge to edge to one another (side by side) and attached to one surface of membrane 38. Membrane 38 may be attached or heat sealed to electrode spacer 20.
- Electrolyte 14 may be supplied from reservoir 17 having a housing 18. A wick 19 may furnish a fluid path for electrolyte 14 from reservoir 17 to electrodes 11-13 and filter papers 15 and 16. Electrolyte 14 may be, for example, a solution of ethylene glycol, water, and a halide salt or acid.
- electrolyte 14 may be a solution of ethylene glycol and water at a ratio of 60 to 40 including a halide such as 0.05 M to 2.0 M hydrocloric acid. 1.0M was found to be the optimum HCl concentration. The ratio of ethylene glycol to water of 60:40 was optimum for low vapor pressure; other ratios may also be used.
- the above electrolyte has a freezing temperature of -80°F and a vapor pressure of less than 0.1 mm Hg when the hydrochloric acid in the electrolyte has a concentration of 0.2 M.
- ethylene glycol may be expressed by the following chemical formula: CH2OHCH2OH.
- the ethylene glycol component in electrolyte 14 solution functions to lower the vapor pressure and the freezing temperature.
- the halide component in electrolyte 14 functions as a supporting electrolyte by providing ions to carry electronic charge between electrodes and functions to inhibit the formation of oxides of the platinum metal at times when the platinum metal is a anodic potential.
- Halides are, for example, a binary compound of a hologen with a more electropositive element or radical. Typical compounds would include the fluorides, chlorides, bromides and iodides.
- Reference electrode 11 and counter electrode 12 may also include a platinum layer, disk, wire or mesh, or include an alloy of platinum or a platinum metal.
- a suitable alloy of platinum may include ruthenium, osmium, rhodium, iridium and palladium or mixtures thereof.
- electrochemical gas sensor 10 also includes a gasket 22, a polyproplylene (PPE) membrane 23, a gasket 25 and metal frame 26.
- a convection barrier 27 which may, for example, be tetrafluoroethylene functions to reduce sensor noise caused by convection in the ambient gas.
- the various elements shown in Fig. 1 may be assembled as shown and positioned much closer together, so that the wide spaces shown in Fig. 1 do not occur in the assembled electrochemical gas sensor 10.
- electrical contact from electrodes 11-13 may be made by means of electrode spacer 20 to respective leads 30-32.
- a control circuit 33 is coupled to leads 30-32 to provide a predetermined voltage on sensing electrode 13 with respect to reference electrode 11.
- control circuit 33 performs this function by providing current to counter electrode 12 which travels through the electrolyte 14 to sensor 13.
- Control circuit 33 may be a temperature compensated potentiostat, well known in the art.
- Control circuit 33 may include circuitry to provide differential pulse voltammetric (DPV) sensing.
- DUV differential pulse voltammetric
- Control circuit 33 also functions to measure the current passing between sensing electrode 13 and counter electrode 12. The current is normally proportional to the concentration of a selected gas, for example, di (2-chloroethyl) sulfide (HD) in the ambient 34.
- An output of control circuit 33 is coupled over lead 39 to indicator circuit 36, which display provides an indication of or a concentration of HD or LEWISITE.
- ambient gas 34 passes through convection barrier 27 through a hole 35 in metal frame 26 and gasket 25 through porous membrane 24 and through thin layer of electrolyte 14 to sensing electrode 13.
- a permselective membrane 37 which is permeable to certain gases, may be utilized between convection barrier 27 and porous membrane 24.
- Fig. 2 is a graph showing the change in output current from sensing electrode 13 on lead 32 as a function of time before and after electrochemical gas sensor 10 is exposed to low levels of HD.
- the ordinate represents change in current in microamperes and the abscissa represents time in minutes.
- Curve 40 shows the response of electrochemical gas sensor 10 to ambient gas 34 having two parts per million of di (2-chloroethyl) sulfide, HD.
- Curve portion 41 of curve 40 represents when no HD was present in ambient gas 34.
- HD was introduced into ambient gas 34 at a concentration of approximately two parts per million.
- HD was removed from ambient gas 34 which corresponds to about 5 minutes.
- curve 40 rises to a value of 29 microamps in 2 minutes.
- Fig. 2 also shows curve 46 which is the response of a prior art electrochemical gas sensor utilizing gold electrodes and having an aqueous caustic electrolyte of 5% potassium hydroxide (KOH) in water.
- Curve 46 represents the response to two parts per million of HD in the ambient gas at time zero. After six minutes the sensor has a response of 36 microamps. The sensor is slow; it requires more than 30 minutes to reach its equilibrium current value at a given concentration of HD. The slow equilibration time is due to the fact that HD is not oxidized directly at the working electrode, but is converted to thiodiglycol in the electrolyte and the thiodiglycol is oxidized at the working electrode.
- Curve portion 47 at 7 minutes represents the decrease in output from the electrochemical gas sensor in response to the removal of HD at 5 minutes.
- Fig. 3 shows the response of a laboratory electrochemical cell to pure liquid agent HD as a function of the voltage on the sensing electrode using DPV sensing.
- the laboratory cell used herein was a Model EC-219, manufactured by the IBM Corporation, Armonk, New York.
- the ordinant represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE).
- the counter electrode was a platinum wire and the sensing electrode was a platinum disk.
- the electrolyte included a solution of ethylene glycol, water, (in a ratio 60:40), and 1.0 M of hydrochloric acid.
- Agent HD was introduced into the electrolyte with a syringe.
- curve 50 shows the output from the sensing electrode as the voltage on the sensing electrode is raised from 0 to .95 volts.
- oxidation peak for HD occurs at 0.87V shown by curve portion 52.
- Fig. 4 shows the response of the laboratory electrochemical cell as described above (Fig. 3) in total absence of agent HD as a function of the voltage on the sensing electrode using DPV sensing.
- the ordinate represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE). No significant current flows between 0.0-0.9V in the absence of HD as shown by curve 55.
- Fig. 5 shows the response of the laboratory electrochemical cell in the absence of HD as described above, except the electrolyte included a solution of ethylene glycol, water, (in ratio 60:40), and 1.0 M of sulfuric acid, H2SO4, a typical non-halide electrolyte.
- the ordinate represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE).
- Significant background current flows between 0.0-0.9V in the absence of HD as shown by curve 58.
- a background current peak occurs at 0.49V as shown by curve portion 59.
- the background current increases substantially above .8V as shown by curve portion 60.
- the current peak at 0.49V is believed due to the oxidation of the platinum sensing electrode surface. This current peak has two deleterious effects if this electrolyte containing H2SO4 is used in electrochemical gas sensor 10 shown in Fig. 1. First, the current peak at 0.49V would cause a large initial current in the absence of HD if electrochemical gas sensor 10 is set at 0.87V to detect HD. The large initial current in the absence of HD would reduce the accuracy of the HD measurement significantly, since the large initial current must be subtracted from the total current to determine the current due to HD. Also, since the background current fluctuates with several environmental conditions, it cannot be subtracted accurately.
- the reaction responsible for the 0.49V current peak will result in a slow build up of platinum oxide on the surface of the sensing electrode of electrochemical gas sensor 10 set at 0.87V to detect HD. Since HD is only detected on a bare platinum electrode surface, not one covered with platinum oxide, a sensor set at 0.87V vs. SCE to detect HD will slowly fail as its sensing electrode is deactivated. Similar problems have occurred when other non-halide electrolytes, such as phosphoric and nitric acids, were tested. The halide is believed to inhibit the formation of platinum oxides which form on platinum electrodes in non-halide electrolytes at high anodic potentials. This phenomenon was investigated for chlorides in a publication by M. W. Schur and J. L. Weininger, entitled “Dissolution of Oxygen Layers on Platinum in Chloride Solutions", supra.
- electrochemical gas sensor 10 with electrolyte 14 is a major improvement over prior art HD sensors.
- Table 2 shows the interfence rejection of electrochemical gas sensor 10 which is set to alarm at 10 ug/l HD to the 15 interference listed in Table 1.
- the words "will not alarm” represents that the interferent will not alarm at its saturated vapor pressure at 20°C temperature.
- An electrochemical gas sensor for detecting selected compounds in a gaseous environment comprising a sensing electrode including platinum or a platinum alloy in contact with an electrolyte, a reference electrode in contact with the electrolyte, and means for maintaining the potential of the sensing electrode with respect to the potential of the reference electrode, wherein the electrolyte includes a solution of ethylene glycol, water, and a halide, for example hydrochloric acid, whereby the selected compounds are oxidized at the sensing electrode.
- An alternate electrolyte includes water and a halide.
- the sensor is useful for detecting low levels, for example, 2 parts per million (2 PPM) of alkyl sulfides, di (2-chloroethyl) sulfide (HD) and 2-chlorovinyldichloroarsine (LEWISITE).
- 2 PPM 2 parts per million
- HD di (2-chloroethyl) sulfide
- LWISITE 2-chlorovinyldichloroarsine
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biochemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Molecular Biology (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Measuring Oxygen Concentration In Cells (AREA)
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
Description
- This invention was made with Government support under Contract No. DAAK-11-84-C-0060 awarded by the U. S. Army. The Government has certain rights in this invention.
- Cross reference is made to US application Serial No. 697,595, filed on February 1, 1985, entitled "Electrochemical Gas Sensor by J. C. Schmidt, D. N. Campbell and S. B. Clay and assigned to the assigned herein which is directed to a three electrode sensor utilizing a nonaqueous electrolyte namely, n-methyl-2-pyrrolidone and a salt soluble therein.
- Cross reference is made to a U.S. application serial no. 710,757 filed on March 11, 1985, which is a divisional application of serial no. 541,630 filed on October 13, 1983, now abandoned, entitled "Electrochemical Gas Sensor" by J. C. Schmidt, D. N. Campbell and S. B. Clay and assigned to the assignee herein which describes a three electrode gas sensor and a nonaqueous electrolyte n-methyl-2-pyrrolidone, with a conductive salt, such as tetrabutyl ammonium tetrafluoroborate.
- This invention relates to electrochemical gas sensors and more particularly to a sensor for sensing alkyl sulfides and lewisite in a gaseous environment.
- U.S. Patent 3,776,832 to Oswin et al. which issued on December 4, 1973, and was reissued as re: 31,916 on June 18, 1985, describes a three electrode electrochemical gas sensor using an aqueous electrolyte which can be adapted to measure oxidizable or reducible gases, such as chlorine, CO, Cl₂ and hydrazine, as well as other gases. This particular known cell has two shortcomings. First, the aqueous electrolyte which has a limited service life due to evaporation of the electrolyte, and second, the temperature range within which the cell can operate is limited due to the possibility of freezing of the electrolyte.
- The shortcomings noted above as a result of using an aqueous electrolyte have been recognized for some time. U.S. Patent 4,184,937, which issued on January 22, 1980, to H. Tataria et al. entitled "Electrochemical Cell for the Detection of Chlorine", describes a three electrode cell with a non-aqueous electrolyte consisting preferably of lithium perchlorate dissolved in an organic solvent selected from the group consisting of gamma-butyrolactone and propylene carbonate. The non-aqueous electrolyte has a considerably lower freezing point and vapor pressure than an aqueous electrolyte. The electrodes for use in the two or three electrode electrochemical cells are comprised of either gold or platinum black.
- In U.S. Patent 4,201,634, which issued on May 6, 1980, to J. R. Stetter entitled "Method for the Detection of Hydrazine", a three electrode electrochemical cell is described using an aqueous alkaline electrolyte (KOH) in contact with the sensing electrode. The sensing electrode comprises a noble metal calayst bonded to a hydrophobic material to provide a diffusion electrode. The catalyst is described as rhodium or gold and the hydrophobic material is described as polytetrafluoroethylene.
- It is possible to use an aqueous sensor of the type described in U.S. Patent 3,776,832 to detect chemical warfare agents such as mustard gas (di (2-chloroethyl) sulfide, designated HD). For example, a sensor containing a caustic aqueous electrolyte in contact with a gold sensing electrode has been used to detect the presence of HD. However, the aqueous electrochemical sensor has three disadvantages when used for the detection of HD. First, the sensor is slow; it requires more than 30 minutes to reach its equilibrium current value at a given concentration of HD. The slow equilibration time is due to the fact that HD is not oxidized directly at the working electrode, but is converted to thiodiglycol in the electrolyte and then the alcohol functional group of the thiodiglycol is oxidized at the working electrode. The half life of the hydrolysis of HD to thiodiglycol is greater than five minutes. Secondly, the sensor suffers from numerous false alarms, since the aqueous HD sensor is sensitive to aliphatic alcohols, aldehydes, and several other gases in addition to alkyl sulfides. Third, the sensor has a relatively short life due to absorption of CO₂ from the air by the caustic electrolyte.
- In a paper entitled "Diffusion Currents at Cylindrical Electrodes. A Study of Organic Sulfides." by M. M. Nicholson, J. Am. Chem Soc. 76: 2539-2545, 1954, the author suggested that many dialkyl sulfides could be oxidized in methanolic HCl solutions. The high vapor pressure of methanol of 100 mm Hg at 21°C would result in a sensor with a reduced service life due to excessive electrolyte evaporation.
- It is well established in the literature that dialkyl sulfides similar to HD can be oxidized to form the corresponding sulfoxides and sulfones.
- In a publication by M. W. Breiter and J. L. Weininger entitled "Dissolution of Oxygen Layers on Platinum in Chloride Solutions", J. Electro Chem. Soc., 109(12): 1135-1138, 1962, the dissolution of oxygen layers on platinum in dilute and concentrated chloride solutions is described.
- In a publication by J. A. Plambeck, published in Electro Analytical Chemistry, Wiley-Interscience, pages 50-51, New York, N. Y. (1982), a potentiostat is described for maintaining a sensing electrode of an electrochemical cell at a fixed potential with respect to its reference electrode.
- It is therefore desirable to use an electrolyte in the electrochemical gas sensor which permits direct oxidation of alkyl sulfides, thereby providing a fast response time.
- It is further desirable to provide an electrolyte in an electrochemical gas sensor which improves the detection and specificity of alkyl sulfides.
- It is further desirable to provide an electrolyte which evaporates slowly due to a low vapor pressure to extend the life of the electrochemical gas sensor.
- It is further desirable to use an electrolyte which has a low freezing temperature to permit sensing down to the freezing temperature.
- It is further desirable to use an electrolyte which is not degraded by CO₂ uptake from the air.
- An apparatus is described for detecting selected compounds in a gaseous environment comprising a sensing electrode including platinum or alloys thereof in contact with an electrolyte, the electrolyte being exposed to the gaseous environment, a reference electrode in contact with the electrolyte, and means for maintaining the potential of the sensing electrode with respect to the potential of the reference electrode, wherein the electrolyte includes a solution of ethylene glycol, water, and a halide, whereby said selected, for example, alkyl sulfides and LEWISITE compounds are oxidized at the sensing electrode. In an alternate embodiment the electrolyte includes a solution of water and a halide.
-
- Fig. 1 is a schematic diagram of one embodiment of the invention.
- Fig. 2 is a graph showing the response of the embodiment of Fig. 1 and of a prior art sensor to di (2-chloroethyl) sulfide, designated HD as a function of time.
- Fig. 3 is a graph showing the response of an experimental laboratory cell to di (2-choroethyl) sulfide (HD) as a function of the sensing electrode voltage.
- Fig. 4 is a graph showing the response of a laboratory electrochemical cell in the absence of HD as a function of the sensing electrode voltage.
- Fig. 5 is a graph showing the response of a laboratory electrochemical cell in the absense of HD as a function of the sensing electrode voltage.
- Referring to Fig. 1, an
electrochemical gas sensor 10 is shown.Electrochemical gas sensor 10 includes a reference electrode 11, acounter electrode 12 and asensing electrode 13.Sensing electrode 13 may be attached to one side of aporous membrane 24 which may be for example tetrafluoroethylene. The other side ofmembrane 24 is exposed to the gaseous environment 34 to be monitored.Sensing electrode 13 may be for example a platinum wire mesh, a layer of platinum vacuum sputtered directly on tomembrane 24, or a composite structure fabricated by sintering a mixture of platinum powder and small polytetrafloroethylene (PTFE) particles tomembrane 24. Reference electrode 11,counter electrode 12, and sensingelectrode 13 are spaced apart from each other and in contact withelectrolyte 14. Contact may be maintained by means offilter paper electrolyte 14. Reference electrode 11 andcounter electrode 12 may be positioned edge to edge to one another (side by side) and attached to one surface ofmembrane 38.Membrane 38 may be attached or heat sealed toelectrode spacer 20. -
Electrolyte 14 may be supplied fromreservoir 17 having ahousing 18. Awick 19 may furnish a fluid path forelectrolyte 14 fromreservoir 17 to electrodes 11-13 andfilter papers Electrolyte 14 may be, for example, a solution of ethylene glycol, water, and a halide salt or acid. For example,electrolyte 14 may be a solution of ethylene glycol and water at a ratio of 60 to 40 including a halide such as 0.05 M to 2.0 M hydrocloric acid. 1.0M was found to be the optimum HCl concentration. The ratio of ethylene glycol to water of 60:40 was optimum for low vapor pressure; other ratios may also be used. The above electrolyte has a freezing temperature of -80°F and a vapor pressure of less than 0.1 mm Hg when the hydrochloric acid in the electrolyte has a concentration of 0.2 M. - It is well known in the art that ethylene glycol may be expressed by the following chemical formula: CH₂OHCH₂OH. The ethylene glycol component in
electrolyte 14 solution functions to lower the vapor pressure and the freezing temperature. The halide component inelectrolyte 14 functions as a supporting electrolyte by providing ions to carry electronic charge between electrodes and functions to inhibit the formation of oxides of the platinum metal at times when the platinum metal is a anodic potential. Halides are, for example, a binary compound of a hologen with a more electropositive element or radical. Typical compounds would include the fluorides, chlorides, bromides and iodides. An electrolyte consisting of an aqueous HCl solution may be used but appears to be less desirable than an aqueous-glycol HCl solution. Reference electrode 11 andcounter electrode 12 may also include a platinum layer, disk, wire or mesh, or include an alloy of platinum or a platinum metal. A suitable alloy of platinum may include ruthenium, osmium, rhodium, iridium and palladium or mixtures thereof. - As shown in Fig. 1
electrochemical gas sensor 10 also includes agasket 22, a polyproplylene (PPE)membrane 23, agasket 25 andmetal frame 26. A convection barrier 27 which may, for example, be tetrafluoroethylene functions to reduce sensor noise caused by convection in the ambient gas. The various elements shown in Fig. 1 may be assembled as shown and positioned much closer together, so that the wide spaces shown in Fig. 1 do not occur in the assembledelectrochemical gas sensor 10. In fact, electrical contact from electrodes 11-13 may be made by means ofelectrode spacer 20 to respective leads 30-32. Acontrol circuit 33 is coupled to leads 30-32 to provide a predetermined voltage on sensingelectrode 13 with respect to reference electrode 11. Typically,control circuit 33 performs this function by providing current to counterelectrode 12 which travels through theelectrolyte 14 tosensor 13.Control circuit 33 may be a temperature compensated potentiostat, well known in the art.Control circuit 33 may include circuitry to provide differential pulse voltammetric (DPV) sensing.Control circuit 33 also functions to measure the current passing betweensensing electrode 13 andcounter electrode 12. The current is normally proportional to the concentration of a selected gas, for example, di (2-chloroethyl) sulfide (HD) in the ambient 34. An output ofcontrol circuit 33 is coupled overlead 39 toindicator circuit 36, which display provides an indication of or a concentration of HD or LEWISITE. - In operation, ambient gas 34 passes through convection barrier 27 through a
hole 35 inmetal frame 26 andgasket 25 throughporous membrane 24 and through thin layer ofelectrolyte 14 to sensingelectrode 13. Apermselective membrane 37, which is permeable to certain gases, may be utilized between convection barrier 27 andporous membrane 24. - Fig. 2 is a graph showing the change in output current from sensing
electrode 13 onlead 32 as a function of time before and afterelectrochemical gas sensor 10 is exposed to low levels of HD. In Fig. 2 the ordinate represents change in current in microamperes and the abscissa represents time in minutes.Curve 40 shows the response ofelectrochemical gas sensor 10 to ambient gas 34 having two parts per million of di (2-chloroethyl) sulfide, HD.Curve portion 41 ofcurve 40 represents when no HD was present in ambient gas 34. Atpoint 42, corresponding to about 0 minutes, HD was introduced into ambient gas 34 at a concentration of approximately two parts per million. Atpoint 44 oncurve 40, HD was removed from ambient gas 34 which corresponds to about 5 minutes. As shown in Fig. 2,curve 40 rises to a value of 29 microamps in 2 minutes. - Fig. 2 also shows
curve 46 which is the response of a prior art electrochemical gas sensor utilizing gold electrodes and having an aqueous caustic electrolyte of 5% potassium hydroxide (KOH) in water.Curve 46 represents the response to two parts per million of HD in the ambient gas at time zero. After six minutes the sensor has a response of 36 microamps. The sensor is slow; it requires more than 30 minutes to reach its equilibrium current value at a given concentration of HD. The slow equilibration time is due to the fact that HD is not oxidized directly at the working electrode, but is converted to thiodiglycol in the electrolyte and the thiodiglycol is oxidized at the working electrode.Curve portion 47 at 7 minutes represents the decrease in output from the electrochemical gas sensor in response to the removal of HD at 5 minutes. - Fig. 3 shows the response of a laboratory electrochemical cell to pure liquid agent HD as a function of the voltage on the sensing electrode using DPV sensing. The laboratory cell used herein was a Model EC-219, manufactured by the IBM Corporation, Armonk, New York. In Fig. 3 the ordinant represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE). The counter electrode was a platinum wire and the sensing electrode was a platinum disk. The electrolyte included a solution of ethylene glycol, water, (in a ratio 60:40), and 1.0 M of hydrochloric acid. Agent HD was introduced into the electrolyte with a syringe.
- In Fig. 3,
curve 50 shows the output from the sensing electrode as the voltage on the sensing electrode is raised from 0 to .95 volts. As shown in Fig. 3 oxidation peak for HD occurs at 0.87V shown bycurve portion 52. - Experimental laboratory cells such as the IBM EC-219 are typically used by those skilled in the art to study, in detail, the reactions which take place in an electrochemical sensor.
- Fig. 4 shows the response of the laboratory electrochemical cell as described above (Fig. 3) in total absence of agent HD as a function of the voltage on the sensing electrode using DPV sensing. In Fig. 4 the ordinate represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE). No significant current flows between 0.0-0.9V in the absence of HD as shown by
curve 55. - Fig. 5 shows the response of the laboratory electrochemical cell in the absence of HD as described above, except the electrolyte included a solution of ethylene glycol, water, (in ratio 60:40), and 1.0 M of sulfuric acid, H₂SO₄, a typical non-halide electrolyte. In Fig. 5 the ordinate represents current in microamperes and the abscissa represents the voltage of the sensing electrode with respect to a saturated calomel reference electrode (SCE). Significant background current flows between 0.0-0.9V in the absence of HD as shown by
curve 58. A background current peak occurs at 0.49V as shown bycurve portion 59. The background current increases substantially above .8V as shown bycurve portion 60. - The current peak at 0.49V is believed due to the oxidation of the platinum sensing electrode surface. This current peak has two deleterious effects if this electrolyte containing H₂SO₄ is used in
electrochemical gas sensor 10 shown in Fig. 1. First, the current peak at 0.49V would cause a large initial current in the absence of HD ifelectrochemical gas sensor 10 is set at 0.87V to detect HD. The large initial current in the absence of HD would reduce the accuracy of the HD measurement significantly, since the large initial current must be subtracted from the total current to determine the current due to HD. Also, since the background current fluctuates with several environmental conditions, it cannot be subtracted accurately. Second, the reaction responsible for the 0.49V current peak will result in a slow build up of platinum oxide on the surface of the sensing electrode ofelectrochemical gas sensor 10 set at 0.87V to detect HD. Since HD is only detected on a bare platinum electrode surface, not one covered with platinum oxide, a sensor set at 0.87V vs. SCE to detect HD will slowly fail as its sensing electrode is deactivated. Similar problems have occurred when other non-halide electrolytes, such as phosphoric and nitric acids, were tested. The halide is believed to inhibit the formation of platinum oxides which form on platinum electrodes in non-halide electrolytes at high anodic potentials. This phenomenon was investigated for chlorides in a publication by M. W. Breiter and J. L. Weininger, entitled "Dissolution of Oxygen Layers on Platinum in Chloride Solutions", supra. -
- The alcohols, acetone, and ethylene generate strong signals in prior art aqueous sensors, but do not effect the
electrochemical gas sensor 10 withelectrolyte 14. This is a major advance, since these materials, especially the aliphatic alcohols, are normally present in many situations where HD is a threat. -
- An electrochemical gas sensor has been described for detecting selected compounds in a gaseous environment comprising a sensing electrode including platinum or a platinum alloy in contact with an electrolyte, a reference electrode in contact with the electrolyte, and means for maintaining the potential of the sensing electrode with respect to the potential of the reference electrode, wherein the electrolyte includes a solution of ethylene glycol, water, and a halide, for example hydrochloric acid, whereby the selected compounds are oxidized at the sensing electrode. An alternate electrolyte includes water and a halide. The sensor is useful for detecting low levels, for example, 2 parts per million (2 PPM) of alkyl sulfides, di (2-chloroethyl) sulfide (HD) and 2-chlorovinyldichloroarsine (LEWISITE).
Claims (10)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US79558385A | 1985-11-06 | 1985-11-06 | |
US795583 | 1985-11-06 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0221381A2 true EP0221381A2 (en) | 1987-05-13 |
EP0221381A3 EP0221381A3 (en) | 1987-07-22 |
EP0221381B1 EP0221381B1 (en) | 1991-01-02 |
Family
ID=25165907
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19860113890 Expired EP0221381B1 (en) | 1985-11-06 | 1986-10-07 | Electrochemical gas sensor |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0221381B1 (en) |
JP (1) | JPS62113056A (en) |
DE (1) | DE3676434D1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0859228A2 (en) * | 1997-02-17 | 1998-08-19 | Hitachi, Ltd. | Electrochemical analyzing apparatus |
EP1886128B1 (en) * | 2005-05-11 | 2011-03-09 | Dart Sensors Limited | Electrochemical sensors |
EP3194946A4 (en) * | 2014-09-18 | 2018-04-04 | Case Western Reserve University | Sensor for volatile organic compound detection |
US10175191B2 (en) * | 2013-09-09 | 2019-01-08 | Dräger Safety AG & Co. KGaA | Electrochemical gas sensor, liquid electrolyte and use of a liquid electrolyte in an electrochemical gas sensor |
US10883958B2 (en) * | 2013-09-09 | 2021-01-05 | Dräger Safety AG & Co. KGaA | Liquid electrolyte for an electrochemical gas sensor |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2010085130A (en) * | 2008-09-30 | 2010-04-15 | Riken Keiki Co Ltd | Electrochemical gas sensor and operation electrode thereof |
JP2010197260A (en) * | 2009-02-26 | 2010-09-09 | Riken Keiki Co Ltd | Electrochemical gas sensor for lewisite detection and operation electrode thereof |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0097553A2 (en) * | 1982-06-04 | 1984-01-04 | The Bendix Corporation | Hydrophilic membrane oxygen sensor |
EP0138161A2 (en) * | 1983-10-13 | 1985-04-24 | Environmental Technologies Group, Inc. | Electrochemical gas sensor |
USRE31916E (en) * | 1970-11-10 | 1985-06-18 | Becton Dickinson & Company | Electrochemical detection cell |
GB2164156A (en) * | 1984-08-30 | 1986-03-12 | Mine Safety Appliances Co | Electrochemical gas sensor |
EP0190566A2 (en) * | 1985-02-01 | 1986-08-13 | Allied Corporation | Electrochemical gas sensor |
-
1986
- 1986-10-07 EP EP19860113890 patent/EP0221381B1/en not_active Expired
- 1986-10-07 DE DE8686113890T patent/DE3676434D1/en not_active Expired - Lifetime
- 1986-11-06 JP JP61262893A patent/JPS62113056A/en active Pending
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
USRE31916E (en) * | 1970-11-10 | 1985-06-18 | Becton Dickinson & Company | Electrochemical detection cell |
EP0097553A2 (en) * | 1982-06-04 | 1984-01-04 | The Bendix Corporation | Hydrophilic membrane oxygen sensor |
EP0138161A2 (en) * | 1983-10-13 | 1985-04-24 | Environmental Technologies Group, Inc. | Electrochemical gas sensor |
GB2164156A (en) * | 1984-08-30 | 1986-03-12 | Mine Safety Appliances Co | Electrochemical gas sensor |
EP0190566A2 (en) * | 1985-02-01 | 1986-08-13 | Allied Corporation | Electrochemical gas sensor |
Non-Patent Citations (1)
Title |
---|
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, vol. 109, no. 12, 1962, pages 1135-1138; M.W. BREITER et al.: "Dissolution of oxygen layers on platinum in chloride solutions" * |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0859228A2 (en) * | 1997-02-17 | 1998-08-19 | Hitachi, Ltd. | Electrochemical analyzing apparatus |
EP0859228A3 (en) * | 1997-02-17 | 1999-02-10 | Hitachi, Ltd. | Electrochemical analyzing apparatus |
EP1886128B1 (en) * | 2005-05-11 | 2011-03-09 | Dart Sensors Limited | Electrochemical sensors |
US10175191B2 (en) * | 2013-09-09 | 2019-01-08 | Dräger Safety AG & Co. KGaA | Electrochemical gas sensor, liquid electrolyte and use of a liquid electrolyte in an electrochemical gas sensor |
US10883958B2 (en) * | 2013-09-09 | 2021-01-05 | Dräger Safety AG & Co. KGaA | Liquid electrolyte for an electrochemical gas sensor |
EP3194946A4 (en) * | 2014-09-18 | 2018-04-04 | Case Western Reserve University | Sensor for volatile organic compound detection |
US10935513B2 (en) | 2014-09-18 | 2021-03-02 | Case Western Reserve University | Sensor for volatile organic compound detection |
Also Published As
Publication number | Publication date |
---|---|
EP0221381B1 (en) | 1991-01-02 |
EP0221381A3 (en) | 1987-07-22 |
JPS62113056A (en) | 1987-05-23 |
DE3676434D1 (en) | 1991-02-07 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
EP0163728B1 (en) | Electrochemical sensing of carbon monoxide | |
US4563249A (en) | Electroanalytical method and sensor for hydrogen determination | |
US4568445A (en) | Electrode system for an electro-chemical sensor for measuring vapor concentrations | |
Cao et al. | The properties and applications of amperometric gas sensors | |
US7279080B2 (en) | Gas sensors | |
US4025412A (en) | Electrically biased two electrode, electrochemical gas sensor with a H.sub.2 | |
US4474648A (en) | Gas sensor | |
US5667653A (en) | Electrochemical sensor | |
US4707242A (en) | Electrochemical cell for the detection of noxious gases | |
WO1993021522A1 (en) | Polymeric film-based electrochemical sensor apparatus | |
US6001240A (en) | Electrochemical detection of hydrogen cyanide | |
US6423209B1 (en) | Acid gas measuring sensors and method of using same | |
US4595486A (en) | Electrochemical gas sensor | |
EP0221381B1 (en) | Electrochemical gas sensor | |
AU2016202181B2 (en) | Gas sensor using an ionic liquid electrolyte | |
US3689394A (en) | Oxygen sensors | |
US5746900A (en) | Non-aqueous amperometric multi-gas sensor | |
WO1999001756A1 (en) | Electrochemical sensor approximating dose-response behavior and method of use thereof | |
GB2075197A (en) | Electrochemical gas sensor | |
JP2001289816A (en) | Controlled potential electrolysis type gas sensor | |
Pfenning et al. | Electrochemical investigation of amperometric ammonia gas sensors | |
JP3307827B2 (en) | Potentiometric electrolytic ammonia gas detector | |
WO2000039571A9 (en) | Electrochemical gas sensor and gas sensing method | |
Do et al. | Anodic oxidation of nitric oxide on Au/Nafion®: Kinetics and mass transfer | |
Gas | Amperometric gas sensors |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
AK | Designated contracting states |
Kind code of ref document: A2 Designated state(s): DE GB |
|
PUAL | Search report despatched |
Free format text: ORIGINAL CODE: 0009013 |
|
AK | Designated contracting states |
Kind code of ref document: A3 Designated state(s): DE GB |
|
17P | Request for examination filed |
Effective date: 19880307 |
|
17Q | First examination report despatched |
Effective date: 19881013 |
|
RAP1 | Party data changed (applicant data changed or rights of an application transferred) |
Owner name: ENVIRONMENTAL TECHNOLOGIES GROUP, INC. |
|
GRAA | (expected) grant |
Free format text: ORIGINAL CODE: 0009210 |
|
AK | Designated contracting states |
Kind code of ref document: B1 Designated state(s): DE GB |
|
REF | Corresponds to: |
Ref document number: 3676434 Country of ref document: DE Date of ref document: 19910207 |
|
PLBE | No opposition filed within time limit |
Free format text: ORIGINAL CODE: 0009261 |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT |
|
26N | No opposition filed | ||
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: GB Payment date: 19930928 Year of fee payment: 8 |
|
PGFP | Annual fee paid to national office [announced via postgrant information from national office to epo] |
Ref country code: DE Payment date: 19931011 Year of fee payment: 8 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: GB Effective date: 19941007 |
|
GBPC | Gb: european patent ceased through non-payment of renewal fee |
Effective date: 19941007 |
|
PG25 | Lapsed in a contracting state [announced via postgrant information from national office to epo] |
Ref country code: DE Effective date: 19950701 |